Lighting apparatus and projection-type image display apparatus

ABSTRACT

A lighting apparatus includes: a light source generating a first color component light; a separation element partially transmitting the first color component light, partially reflecting the first color component light, and transmitting a second color component light different from the first color component light at a certain moment; an illuminant excited by the first color component light transmitted through the separation element to generate the second color component light; and an optical system combining the first color component light made incident on the separation element from the light source and reflected by the separation element with the second color component light made incident on the separation element from the illuminant and transmitted through the separation element. The separation element is configured to have variable transmittance and reflectance with respect to the first color component light.

BACKGROUND 1. Technical Field

The present disclosure relates to a lighting apparatus generating anillumination light for a light modulation element etc. of aprojection-type image display apparatus and also relates to aprojection-type image display apparatus including such a lightingapparatus.

2. Related Art

Projection-type image display apparatuses are widely used for projectingimages on large screens in movies and conference presentations. Theprojection-type image display apparatuses can project a distortion-freeimage focused even in the periphery, mainly on a substantially flatwhite projection surface.

A high light intensity white lamp light source such as a xenon lamp andan extra high-pressure mercury lamp has been conventionally used as alight source of a projection-type image display apparatus. However, thelamp light source must be replaced every few thousand hours due toservice life and becomes completely unable to display an image in theworst case when reaching the end of the service life, therefore having aproblem in maintainability during long-term use.

Solid-state light source elements such as light emitting diodes andlaser diodes having a longer service life are used instead of the lamplight source in recently developed lighting apparatuses andprojection-type image display apparatuses. The solid-state light sourceelements reduce the frequency of, or eliminate the need for, thereplacement and therefore significantly improve the maintainability.Additionally, due to the narrow spectral distribution characteristics ofthe solid-state light source element, a projection-type image displayapparatus having a wide color gamut can be achieved. Particularly, whena laser diode is used as a light source, a light utilization efficiencycan be improved due to smaller spread of the light from the lightsource. A projection-type image display apparatus including a blue laserdiode and a phosphor is also provided, and when luminance isparticularly required, a blue light is applied to the phosphor togenerate another color component light.

SUMMARY

An object of the present disclosure is to provide a lighting apparatusand a projection-type image display apparatus capable of selectivelyimproving a spectral characteristic of a certain color component lightwith a simple configuration without requiring significant changes inconfigurations of existing illumination and projection-type imagedisplay apparatuses.

A lighting apparatus according to an aspect of the present disclosureincludes: a light source generating a first color component light; aseparation element partially transmitting the first color componentlight, partially reflecting the first color component light, andtransmitting a second color component light different from the firstcolor component light at a certain moment; an illuminant excited by thefirst color component light transmitted through the separation elementto generate the second color component light; and an optical systemcombining the first color component light made incident on theseparation element from the light source and reflected by the separationelement with the second color component light made incident on theseparation element from the illuminant and transmitted through theseparation element. The separation element is configured to havevariable transmittance and reflectance with respect to the first colorcomponent light.

The lighting apparatus and the projection-type image display apparatusaccording to an aspect of the present disclosure can selectively improvea spectral characteristic of a certain color component light with asimple configuration without requiring significant changes inconfigurations of existing illumination and projection-type imagedisplay apparatuses.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing an exemplary configuration of aprojection-type image display apparatus 1 according to a firstembodiment.

FIG. 2 is a graph showing an exemplary transmission characteristic of adichroic mirror 106 of FIG. 1;

FIG. 3 is a front view showing an exemplary configuration of a phosphorwheel device 210 of FIG. 1;

FIG. 4 is a side view showing an exemplary configuration of the phosphorwheel device 210 of FIG. 1;

FIG. 5 is a schematic diagram showing an exemplary configuration of adichroic mirror 220 of FIG. 1;

FIG. 6 is a graph showing an exemplary transmission characteristic ofthe dichroic mirror 220 of FIG. 1;

FIG. 7 is a front view showing an exemplary configuration of a filterwheel device 240 of FIG. 1;

FIG. 8 is a side view showing the exemplary configuration of the filterwheel device 240 of FIG. 1;

FIG. 9 is a diagram showing spectral characteristics of a dichroic film242 d of FIG. 7;

FIG. 10 is an x-y chromaticity diagram of the CIE1931 color space of theprojection-type image display apparatus 1 of FIG. 1;

FIG. 11 is a schematic diagram showing a path of blue light when thespectral characteristic of blue light is improved in the projection-typeimage display apparatus 1 of FIG. 1;

FIG. 12 is a schematic diagram showing a path of blue light when thespectral characteristic of blue light is not improved in theprojection-type image display apparatus 1 of FIG. 1.

FIG. 13 is a schematic diagram showing an exemplary configuration of aprojection-type image display apparatus 1A according to a comparativeexample of the first embodiment;

FIG. 14 is a schematic diagram showing an exemplary configuration of adichroic mirror 220B according to a first modification of the firstembodiment.

FIG. 15 is a schematic diagram showing an exemplary configuration of aprojection-type image display apparatus 1C according to a secondmodification of the first embodiment;

FIG. 16 is a front view showing an exemplary configuration of a phosphorwheel device 250 of FIG. 15;

FIG. 17 is a side view showing an exemplary configuration of thephosphor wheel device 250 of FIG. 15;

FIG. 18 is a schematic diagram showing an exemplary configuration of aprojection-type image display apparatus 1D according to a secondembodiment;

FIG. 19 is a graph showing an exemplary transmission characteristic of apolarization beam splitter 235 of FIG. 18;

FIG. 20 is a schematic diagram showing a path of blue light when thespectral characteristic of blue light is improved in the projection-typeimage display apparatus 1D of FIG. 18; and

FIG. 21 is a schematic diagram showing a path of blue light when thespectral characteristic of blue light is not improved in theprojection-type image display apparatus 1D of FIG. 18.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments will now be described in detail with reference to thedrawings as needed. It is noted that detailed description will not beprovided more than necessary in some cases. For example, detaileddescription of already well-known facts and repeated description ofsubstantially the same constituent elements may not be provided. This isfor the purpose of avoiding unnecessary redundancy of the followingdescription and facilitating understanding by those skilled in the art.

The accompanying drawings and the following description are provided forsufficient understanding of the present disclosure by those skilled inthe art, and it is not intended to limit the subject matter described inclaims thereto.

To simplify a device and reduce costs, a conventionally providedprojection-type image display apparatus applies color component lights(e.g., red, green, and blue lights) to a single light modulation elementin a time-division manner to switch and display color componentsdifferent from each other at high speed in frames of images and therebyallows a viewer to perceive full-color images. For example, when a bluesolid-state light source element and a phosphor are used as a lightsource in such a projection-type image display apparatus, generally, ablue light generated by the solid-state light source element is directlyused as the blue light applied to the light modulation element. However,when the luminous efficiency of the solid-state light source element ismaximized, the spectral characteristic of the blue light generated bythe solid-state light source element is not necessarily identical to thepreferable spectral characteristic of the blue light to be projected bythe projection-type image display apparatus. Moreover, the spectralcharacteristic of the blue light exciting the phosphor in a mannermaximizing the luminous efficiency of the phosphor is not necessarilyidentical to the preferable spectral characteristic of the blue light tobe projected by the projection-type image display apparatus. Therefore,considering the luminous efficiencies of the solid-state light sourceelement and the phosphor, this causes a problem that a spectralcharacteristic of blue light of a lighting apparatus and aprojection-type image display apparatus deviates from the preferablespectral characteristic of blue light to be projected by theprojection-type image display apparatus.

To improve the spectral characteristic of blue light, for example, theinvention of JP 2018-054667 A has been proposed. The invention of JP2018-054667 A includes a wavelength selective reflection platereflecting a portion of a blue light and transmitting a remaining bluelight and other color lights, a fluorescent plate excited by the bluelight transmitted through the wavelength selective reflection plate togenerate a green light, and a condensing element condensing the greenlight generated by the fluorescent plate and emitting the green lighttoward the wavelength selective reflection plate. The wavelengthselective reflection plate is disposed on a portion of a phosphor wheel,for example. The invention of JP 2018-054667 A improves the spectralcharacteristic of blue light by combining the blue light reflected bythe wavelength selective reflection plate and the green light generatedby the fluorescent plate and transmitted through the wavelengthselective reflection plate.

The invention of JP 2018-054667 A requires a significant change inconfiguration of an existing projection-type image display apparatus soas to provide the phosphor wheel integrated with the wavelengthselective reflection plate, the reflection plate, and the condensingelement. Therefore, it is desired that a spectral characteristic of acertain color component light can be improved without requiringsignificant changes in configurations of existing illumination andprojection-type image display apparatuses.

In the invention of JP 2018-054667 A, the green light is always combinedwith the blue light. Since the luminous efficiency of the fluorescentplate is less than 100%, using a portion of the blue light to excite thefluorescent plate always reduces the luminance of the blue light ascompared to when the green light is not combined with the blue light. Inthe invention of JP 2018-054667 A requires a significant change in theconfiguration again so as to generate a blue light not being combinedwith a green light. Therefore, it is desired that whether to improve aspectral characteristic of a certain color component light is selectablewith a simple configuration.

The following embodiments provide a lighting apparatus and aprojection-type image display apparatus capable of selectively improvinga spectral characteristic of a certain color component light with asimple configuration without requiring significant changes inconfigurations of existing illumination and projection-type imagedisplay apparatuses.

First Embodiment

A projection-type image display apparatus according to a firstembodiment will now be described with reference to FIGS. 1 to 17

A projection-type image display apparatus including a digitalmicromirror device (hereinafter referred to as “DMD”) as a lightmodulation element will hereinafter be described as a specificembodiment of the present disclosure.

[1-1. Configuration]

FIG. 1 is a schematic diagram showing an exemplary configuration of aprojection-type image display apparatus 1 according to the firstembodiment. The projection-type image display apparatus 1 includes aplurality of laser diodes (LDs) 101, a plurality of collimator lenses102, a condenser lens 103, a concave lens 104, an optical diffuser 105,a dichroic mirror 106, condenser lenses 107, 108, a phosphor wheeldevice 210, a condenser lens 111, a dichroic mirror 220, a drivingdevice 230, condenser lenses 231, 232, a phosphor 233, a concave lens112, a reflective mirror 113, an optical diffuser 114, a convex lens115, a reflective mirror 116, and a condenser lens 117. In thisdescription, these constituent elements of the projection-type imagedisplay apparatus 1 are also referred to as a “lighting apparatus”. Theprojection-type image display apparatus 1 further includes a filterwheel device 240, a rod integrator 121, relay lenses 122, 123, 124, atotal internal reflection prism (TIR prism) 125, a digital micromirrordevice (DMD) 126, and a projection optical system 300. The lightingapparatus described above generates an illumination light to be appliedto the digital micromirror device 126. The digital micromirror device126 spatially modulates the illumination light incident from thelighting apparatus and thereby generates an image light to be projectedonto a screen 400.

The projection-type image display apparatus 1 includes a dichroic mirror220, a driving device 230, condenser lenses 231, 232, and a phosphor 233so as to improve a spectral characteristic of a blue light generated bythe laser diode 101. The phosphor 233 is excited by a blue light togenerate a green light. An optical system includes the dichroic mirror106, the condenser lenses 107, 108, the phosphor wheel device 210, thecondenser lens 111, the dichroic mirror 220, the condenser lenses 231,232, the concave lens 112, the reflective mirror 113, the opticaldiffuser 114, the convex lens 115, and the reflective mirror 116 and isconfigured to combine the blue light generated by the laser diode 101and the green light generated by the phosphor 233 with each other in thedichroic mirror 106.

The LDs 101 generate a linearly polarized blue light in a wavelengthwidth of 447 nm to 462 nm. The LDs 101 are arranged such that anoutgoing light is P-polarized with respect to an incident surface of thedichroic mirror 106. The collimator lens 102 each collimate a lightemitted from the corresponding one LD 101. The condenser lens 103 andthe concave lens 104 constitute an afocal system converging a parallellight to generate a narrower parallel light. Specifically, the condenserlens 103 condenses the parallel light from the plurality of thecollimator lenses 102, and the concave lens 104 collimates the lightfrom the condenser lens 103. The optical diffuser 105 diffuses the lightfrom the concave lens 104. The light passing through the opticaldiffuser 105 is made incident on the dichroic mirror 106.

In this description, the LDs 101 are also referred to as a “lightsource”.

FIG. 2 is a graph showing an exemplary transmission characteristic ofthe dichroic mirror 106 of FIG. 1. The dichroic mirror 106 transmits andreflects respective halves of an S-polarized blue light having awavelength of 465 nm incident thereon and transmits and reflectsrespective halves of a P-polarized blue light having a wavelength of 472nm incident thereon. The dichroic mirror 106 reflects 95% or more ofgreen and red lights regardless of polarization. Since the P-polarizedblue light is incident on the dichroic mirror 106 from the opticaldiffuser 105, the blue light is transmitted through the dichroic mirror106 and proceeds to the condenser lens 107.

The blue light made incident on and transmitted through the dichroicmirror 106 from the optical diffuser 105 is made incident on thecondenser lenses 107, 108 and then condensed on a surface of thephosphor wheel device 210. The focal distance of the condenser lens 108is set to form a converging angle of 40 degrees or less, and acondensing spot is formed near the phosphor wheel device 210.

FIG. 3 is a front view showing an exemplary configuration of thephosphor wheel device 210 of FIG. 1. FIG. 4 is a side view showing anexemplary configuration of the phosphor wheel device 210 of FIG. 1. FIG.3 shows the surface on which the light enters the phosphor wheel device210 from the condenser lens 108. The phosphor wheel device 210 includesa central axis 210X, an aluminum substrate 211, a phosphor layer 212, adriving motor 213, and a slit 214.

The aluminum substrate 211 is a circular substrate including the drivingmotor 213 in a central portion and rotatable around the central axis210X. A reflective film (not shown) is formed on a surface of thealuminum substrate 211, and a phosphor layer 212 is further formed on asurface of the reflective film. The reflective film is a metal layer ora dielectric film reflecting visible light. The slit 214 is disposed ina portion of the aluminum substrate 211. The phosphor layer 212 isprovided with a Ce-activated YAG-based yellow phosphor excited by a bluelight to generate a yellow light containing wavelength components ofgreen and red lights. A typical chemical composition of the crystalmatrix of this yellow phosphor is Y₃Al₅O₁₂. Although the phosphor layer212 is formed substantially in a ring shape, the slit 214 fortransmitting the blue light is disposed in a portion of the ring withoutthe phosphor layer 212.

In this description, the phosphor wheel device 210 is also referred toas a “first phosphor wheel device”.

The phosphor layer 212 is excited by the spot light from the condenserlens 108 and thereby generates a yellow light containing green and redlights. The phosphor wheel device 210 can rotate the aluminum substrate211 around the central axis 210X to suppress a rise in temperature ofthe phosphor layer 212 due to excitation with the blue light and stablymaintain the fluorescence conversion efficiency. A portion of the greenand red lights generated by the phosphor layer 212 is emitted toward thecondenser lens 108. The green and red lights generated by the phosphorlayer 212 and proceeding toward the reflective film are reflected by thereflective film and emitted toward the condenser lens 108. The green andred lights generated by the phosphor layer 212 are emitted as naturallights having a random polarization state. The green and red lightsemitted from the phosphor layer 212 are condensed again and convertedinto substantially parallel lights by the condenser lenses 108, 107 andare then reflected by the dichroic mirror 106 before proceeding to thecondenser lens 117.

On the other hand, the blue light incident on the slit 214 of thephosphor wheel device 210 from the condenser lens 108 directly passesthrough the slit 214 and is converted by the condenser lens 111 into asubstantially parallel and wide light beam before proceeding to thedichroic mirror 220.

FIG. 5 is a schematic diagram showing an exemplary configuration of thedichroic mirror 220 of FIG. 1. The dichroic mirror 220 includes adichroic coat layer 221 and an AR (anti-reflection) coat layer 222formed on a flat transparent substrate such as glass. The dichroic coatlayer 221 reflects blue light and transmits green light. The AR coatlayer 222 transmits blue light and green light. The region of the ARcoat layer 222 is disposed inside the region of the dichroic coat layer221 and has a size smaller than the spot size of the blue light madeincident on the dichroic mirror 220 from the condenser lens 111 (i.e.,the light source). As a result, the dichroic mirror 220 partiallytransmits the blue light, partially reflects the blue light, andtransmits the green light (described later) generated by the phosphor233 at a certain moment.

FIG. 6 is a graph showing an exemplary transmission characteristic ofthe dichroic mirror 220 of FIG. 1. The dichroic mirror 220 transmits andreflects respective halves of an S-polarized blue light having awavelength of 472 nm incident thereon and transmits and reflectsrespective halves of a P-polarized blue light having a wavelength of 465nm incident thereon. The dichroic mirror 220 transmits 95% or more ofgreen and red lights regardless of polarization. In the example of FIG.1, the blue light incident on the dichroic mirror 220 from the condenserlens 111 has P-polarized light similarly to the blue light incident onthe dichroic mirror 220 from the optical diffuser 105.

In FIG. 5, the shape of the AR coat layer 222 is shown as a circle;however, the shape may be a polygon or other shapes.

In this description, the dichroic mirror 220 is also referred to as a“separation element”. In this description, the dichroic coat layer 221is also referred to as a “first region”, and the AR coat layer 222 isalso referred to as a “second region”.

The driving device 230 moves the dichroic mirror 200 to switch whetherthe blue light incident on the dichroic mirror 200 from the condenserlens 111 is all incident on the dichroic coat layer 221 or partiallyincident on the AR coat layer 222. In the former case, all the bluelight incident on the dichroic mirror 200 from the condenser lens 111 isreflected by the dichroic coat layer 221. On the other hand, in thelatter case, a portion of the blue light incident on the dichroic mirror200 from the condenser lens 111 is transmitted through the AR coat layer222 and the rest is reflected by the dichroic coat layer 221. As aresult, the dichroic mirror 220 is configured to have variabletransmittance and reflectance with respect to blue light.

A large portion of the blue light incident on the dichroic mirror 220from the condenser lens 111 is reflected by the dichroic coat layer 221and converted into a substantially parallel light beam via the concavelens 112, the reflective mirror 113, the optical diffuser 114, and theconvex lens 115. The blue light converted into a substantially parallellight beam by the convex lens 115 is reflected by the reflective mirror116 and made incident on the dichroic mirror 106. The blue lightincident on the dichroic mirror 106 is transmitted through the dichroicmirror 106 and proceeds to the condenser lens 117.

On the other hand, a portion of the blue light incident on the dichroicmirror 220 from the condenser lens 111 is transmitted through the ARcoat layer 222 and condensed on a surface of the phosphor 233 via thecondenser lenses 231, 232. The focal distance of the condenser lens 232is set to form a converging angle of 40 degrees or less, and acondensing spot is formed near the phosphor 233.

The phosphor 233 includes a plate-shaped substrate, a reflective filmformed on a surface of the plate-shaped substrate, and a phosphor layerformed on a surface of the reflective film. The reflective film is ametal layer or a dielectric film reflecting visible light. The phosphor233 is provided with a Ce-activated LAG-based green phosphor excited bya blue light to generate a green light. A typical chemical compositionof the crystal matrix of the green phosphor is Lu₃Al₅O₁₂.

The phosphor 233 is excited by the spot light from the condenser lens232 and thereby generates a green light. A radiator plate (not shown) isdisposed on a back surface of the phosphor 233 and can suppress a risein temperature of the phosphor 233 due to excitation with the blue lightand stably maintain the fluorescence conversion efficiency. A portion ofthe green light generated by the phosphor 233 is emitted toward thecondenser lens 232. The green light generated by the phosphor 233 andproceeding toward the reflective film is reflected by the reflectivefilm and emitted toward the condenser lens 232. The green lightgenerated by the phosphor 233 is emitted as a natural light having arandom polarization state. The green light emitted from the phosphor 233is condensed again and converted into a substantially parallel light bythe condenser lenses 232, 231 and is then transmitted through thedichroic mirror 220 before proceeding to the condenser lens 111.

The green light transmitted through the condenser lens 111 is condensedby the condenser lens 111 and passes through the slit 214 of thephosphor wheel device 210. Subsequently, the green light is convertedinto a substantially parallel light by the condenser lenses 108, 107 andthen reflected by the dichroic mirror 106 before proceeding to thecondenser lens 117.

In this description, the phosphor 233 is also referred to as an“illuminant”. In this description, the blue light generated by the LDs101 is also referred to as a “first color component light”, and thegreen light generated by the phosphor 233 is also referred to as a“second color component light”.

The blue light that made incident on and reflected by the dichroicmirror 220 from the light source and the green light made incident onand transmitted through the dichroic mirror 220 from the phosphor 233are combined with each other in the dichroic mirror 106. In this way, bycombining the green light with the blue light (referred to as “combinedblue light”), a preferable spectral characteristic of the blue light tobe projected by the projection-type image display apparatus 1 can beachieved.

The yellow light containing the green light and the red light generatedby the phosphor layer 212 and the combined blue light containing thegreen light generated by the phosphor 233 are obtained as describedabove, and these color component lights proceed from the dichroic mirror106 to the condenser lens 117. When these color component lights arecombined by time division multiplexing, the lights are visuallyrecognized as a white light. The light incident on the condenser lens117 from the dichroic mirror 106 is condensed onto the filter wheeldevice 240.

FIG. 7 is a front view showing an exemplary configuration of the filterwheel device 240 of FIG. 1. FIG. 8 is a side view showing an exemplaryconfiguration of the filter wheel device 240 of FIG. 1. FIG. 7 shows asurface on which the light enters the filter wheel device 240 from thecondenser lens 117. The filter wheel device 240 includes a central axis240X, a transparent substrate 241, a dichroic film 242, and a drivingmotor 243.

The transparent substrate 241 is a circular substrate including thedriving motor 243 in a central portion and rotationally controllablearound the central axis 240X. The transparent substrate 241 is made upof, for example, a glass plate having a high transmittance over theentire visible range. The dichroic film 242 is formed on a surface ofthe transparent substrate 241 so as to transmit only a desiredwavelength band. For example, as shown in FIG. 7, the dichroic film 242includes four fan-shaped regions, i.e., dichroic films 242 a to 242 d.For example, the dichroic film 242 a transmits only yellow light (greenlight+red light), the dichroic film 242 b transmits only red light, thedichroic film 242 c transmits only green light, and the dichroic film242 d transmits blue light and true green light.

The phosphor wheel device 210 and the filter wheel device 240 arecontrolled to rotate in synchronization with each other. For example,the position of the phosphor layer 212 of FIG. 3 and the positions ofthe dichroic films 242 a to 242 c of FIG. 6 are controlled in atemporally synchronized manner. As a result, the yellow light containingthe green light and the red light emitted from the phosphor layer 212 ofFIG. 3 is respectively separated into the yellow light, the red light,and the green light when passing through the dichroic films 242 a to 242c of FIG. 4. On the other hand, the combined blue light containing thegreen light generated by the phosphor 233 and passing through the slit214 of FIG. 3 has a color component on the long wavelength side of thegreen light cut when passing through the dichroic film 242 d of FIG. 4and is changed to a combined blue light containing a true green lightinstead of the green light. The color component lights respectivelytransmitted through the dichroic films 242 a to 242 d proceed to the rodintegrator 121 of FIG. 1.

FIG. 9 is a diagram showing spectral characteristics of the dichroicfilm 242 d of FIG. 7. FIG. 9 shows the spectral characteristics when thegreen light generated by the phosphor 233 passes through the dichroicfilm 242 d. The green light generated by the phosphor 233 has the colorcomponent on the long wavelength side cut due to passing through thedichroic film 242 d and is converted to have the spectral characteristicof the true green light. The cutoff wavelength of the dichroic film 242d is 552 nm, for example. In this case, the green light after passingthrough the dichroic film 242 d has x-y chromaticity coordinates in theCIE1931 color space: x=0.158, y=0.686, for example.

FIG. 10 is an x-y chromaticity diagram of the CIE 1931 color space ofthe projection-type image display apparatus 1 of FIG. 1. FIG. 10 shows acolor space of Rec. 709 and chromaticity coordinates of the blue lightof the LDs 101. The blue light of the LDs 101 has, for example, a mainwavelength of 456 nm and x-y chromaticity coordinates: x=0.150, y=0.026.The combined blue light including the true green light transmittedthrough the dichroic film 242 d moves in the color space as indicated bya broken line in accordance with an intensity ratio of the blue lightand the true green light. The intensity ratio of the blue light and thetrue green light can be adjusted by the size of the AR coat layer 222 inthe dichroic mirror 220. By adjusting the intensity ratio of the bluelight and the true green light, the spectral characteristic of the bluelight projected by the projection-type image display apparatus 1 can bematched to the coordinates of blue light of Rec. 709: x=0.150, y=0.060.

As described above, the yellow light and the combined blue lightincident on the filter wheel device 240 from the condenser lens 117 areseparated into the red light, the green light, the blue light, and theyellow light by the filter wheel device 240 and proceed to the rodintegrator 121. These red, green, and blue lights show favorable threeprimary colors, and color synthesis of these color component lightsthrough time division multiplexing can provide light emissioncharacteristics with favorable white balance. Furthermore, these colorcomponent lights can be converted into colors having desiredchromaticity coordinates by adjusting on-time and off-time of pixels ofthe DMD 126.

The rod integrator 121 is a solid rod made up of a transparent member ofglass etc. The rod integrator 121 internally reflects an incident lightmultiple times to generate a light having a uniform intensitydistribution. The rod integrator 121 may be a hollow rod having an innerwall made up of a mirror surface.

The relay lenses 122, 123, 124 forms an image of the outgoing light ofthe rod integrator 121 substantially on the DMD 126. The outgoing lightof the rod integrator 121 is transmitted through the relay lenses 122,123, 124 and made incident on the total internal reflection prism (TIRprism) 125. The TIR prism 125 is made up of two prisms 125 b, 125 a andhas a thin air layer (not shown) formed in a plane where the prisms 125b, 125 a are close to each other. The air layer totally reflects thelight emitted from the prism 125 a at an angle greater than a criticalangle. The light incident on the TIR prism 125 a from the relay lens 124is totally reflected by this air layer and forms an image substantiallyon the DMD 126.

The DMD 126 spatially modulates the light incident on the DMD 126 basedon various control signals such as an image signal and generates animage light having a different light intensity for each pixel by timedivision for each of the color component lights. Specifically, the DMD126 has a plurality of movable micromirrors. Each of the micromirrorsbasically corresponds to one pixel. The DMD 126 changes an angle of eachof the micromirrors based on a modulation signal from the control signaland thereby switches whether to direct a reflected light to theprojection optical system 300. When a certain micromirror of the DMD 126is turned on, the light reflected by the micromirror passes through bothof the TIR prisms 125 a, 125 b and is made incident on the projectionoptical system 300 and then projected onto a projection surface of thescreen 400.

The red image light, the green image light, the blue image light, andthe yellow image light respectively generated by time division reach theprojection surface of the screen 400 and are perceived as a full colorimage. In this case, if a time division cycle (frame rate) is slow,color flicker may be perceived by human eyes. Therefore, for example, byusing video data having a high frame rate such as 60 frames/second (60fps) and, for example, driving each cycle from the red light to theyellow light at a triple speed (180 fps) of the frame rate of the videodata, the color flicker can be suppressed.

[1-2. Operation]

As shown in FIG. 5, the dichroic mirror 220 is configured to be movable.This enables switching whether the light incident on the dichroic mirror220 from the condenser lens 111 is received by both the dichroic coatlayer 221 and the AR coat layer 222 (ON state of FIG. 5) or by only thedichroic coat layer 221 (OFF state of FIG. 5).

FIG. 11 is a schematic diagram showing a path of blue light when thespectral characteristic of blue light is improved in the projection-typeimage display apparatus 1 of FIG. 1. FIG. 12 is a schematic diagramshowing a path of blue light when the spectral characteristic of bluelight is not improved in the projection-type image display apparatus 1of FIG. 1. FIG. 11 shows a light path in the ON state of FIG. 5, andFIG. 12 shows a light path in the OFF state of FIG. 5.

In the case of FIG. 11, as described above, the blue light transmittedthrough the dichroic mirror 220 excites the phosphor 233, the blue lightand the green light are combined by the dichroic mirror 106, and thecombined blue light proceeds to the filter wheel device 240. Since theconversion efficiency of the phosphor 233 is less than 100%, theintensity of the combined blue light reaching the filter wheel device240 becomes lower than the intensity of the blue light reaching thedichroic mirror 220 from the LD 101. If such a combined blue light iscombined with the green light, the red light, and the yellow light toadjust the white balance, an overall luminance of a projection light isreduced although the spectral characteristic of the blue light isimproved. Depending on a usage environment, it may be required toincrease the overall luminance of the projection light even if thespectral characteristic of the blue light is reduced. Therefore, asshown in FIG. 12, by blocking the blue light reaching the phosphor 233(the OFF state of FIG. 5), the intensity of the blue light reaching thefilter wheel device 240 can be increased to make the overall luminanceof the projection light higher.

As described above, the projection-type image display apparatus 1according to the embodiment can selectively switch whether to improvethe spectral characteristic of the blue light (or to allow a reductionin the overall luminance of the projection light), by a simpleconfiguration and operation of moving the dichroic mirror 220.

FIG. 13 is a schematic diagram showing an exemplary configuration of aprojection-type image display apparatus 1A according to a comparativeexample of the first embodiment. The projection-type image displayapparatus 1A includes a mirror 220A instead of the dichroic mirror 220,the driving device 230, the condenser lenses 231, 232, and the phosphor233 shown in FIG. 1. According to the first embodiment, the spectralcharacteristic of blue light can be improved with a simple configurationwithout requiring significant changes in configuration of an existingdevice such as the projection-type image display apparatus 1A.

[1-3. Modification]

FIG. 14 is a schematic diagram showing an exemplary configuration of adichroic mirror 220B according to a first modification of the firstembodiment. The projection-type image display apparatus 1 of FIG. 1 mayinclude a dichroic mirror 220B of FIG. 14 instead of the dichroic mirror220 of FIG. 1. The dichroic mirror 220B has multiple AR coat layers 222,223 different in size and is configured to be movable for switchingwhich of the multiple AR coat layers 222, 223 the blue light is incidenton. As a result, when the blue light and the green light are combinedwith each other, the intensity ratio of the color component lights canbe changed.

The dichroic mirror may have three or more AR coat layers different insize.

FIG. 15 is a schematic diagram showing an exemplary configuration of aprojection-type image display apparatus 1C according to a secondmodification of the first embodiment. The projection-type image displayapparatus 1C includes a phosphor wheel device 250 instead of thephosphor 233 of FIG. 1. In the projection-type image display apparatus 1of FIG. 1, the phosphor 233 is fixed and radiates heat by the radiatorplate (not shown) on the back surface thereof. On the other hand, theprojection-type image display apparatus 1C of FIG. 15 uses the rotatingphosphor wheel device 250 so as to further enhance a heat dissipationeffect.

FIG. 16 is a front view showing an exemplary configuration of thephosphor wheel device 250 of FIG. 15. FIG. 17 is a side view showing anexemplary configuration of the phosphor wheel device 250 of FIG. 15.FIG. 16 shows a surface on which the light enters the phosphor wheeldevice 250 from the condenser lens 232. The phosphor wheel device 250includes a central axis 250X, an aluminum substrate 251, a phosphorlayer 252, and a driving motor 253.

The aluminum substrate 251 is a circular substrate including the drivingmotor 253 in a central portion and rotationally controllable around thecentral axis 250X. A reflective film (not shown) is formed on a surfaceof the aluminum substrate 251, and a phosphor layer 252 is furtherformed on a surface of the reflective film. The reflective film is ametal layer or a dielectric film reflecting visible light. The phosphorlayer 252 is provided with a Ce-activated LAG-based yellow phosphorexcited by a blue light to generate a green light. A typical chemicalcomposition of the crystal matrix of this yellow phosphor is Lu₃Al₅O₁₂.The phosphor layer 252 is formed into an annular shape.

In this description, the phosphor wheel device 250 is also referred toas a “second phosphor wheel device”.

The phosphor wheel device 250 does not need to be synchronized with thephosphor wheel device 210 and the filter wheel device 240 and isindependently driven when the blue light is made incident on thephosphor wheel device 250 from the dichroic mirror 220 (the ON state ofFIG. 5). The phosphor wheel device 250 may be stopped when no blue lightis made incident on the phosphor wheel device 250 from the dichroicmirror 220 (the OFF state of FIG. 5). The phosphor wheel device 250 canrotate the aluminum substrate 251 around the central axis 250X tosuppress a rise in temperature of the phosphor layer 252 due toexcitation with the blue light and stably maintain the fluorescenceconversion efficiency.

The color component on the long wavelength side of the green lightgenerated by the phosphor 233 or the phosphor wheel device 250 may becut by the dichroic coat layer 221 of the dichroic mirror 220 instead ofcutting by the dichroic film 242 d of the filter wheel device 240. Inthis case, the dichroic coat layer 221 transmits and reflects respectivehalves of an S-polarized blue light having a wavelength of 472 nmincident thereon and transmits and reflects respective halves of aP-polarized blue light having a wavelength of 465 nm incident thereon.The dichroic coat layer 221 is configured to cut orange and red lightsat a cutoff wavelength of 552 nm. The green light generated by thephosphor 233 or the phosphor wheel device 250 has the color component onthe long wavelength side is cut when passing through the dichroic coatlayer 221 and is converted to the spectral characteristic of true greenlight. The green light after passing through the dichroic coat layer 221has x-y chromaticity coordinates in the CIE1931 color space: x=0.158,y=0.686, for example. In this case, the dichroic film 242 d of thefilter wheel device 240 is provided with a window of an AR coat filmtransmitting visible light. The combined color component light of theblue light and the true green light is transmitted through the dichroicfilm 242 d without changing the spectral characteristic. With thisconfiguration, the filter wheel device 240 can be reduced in cost.

[1-4. Effects]

The lighting apparatus and the projection-type image display apparatusaccording to the first embodiment include the LDs 101, the separationelement, the phosphor 233, and the optical system. The LDs 101 generatethe first color component light. The separation element partiallytransmits the first color component light, partially reflects the firstcolor component light, and transmits the second color component lightdifferent from the first color component light at a certain moment. Thephosphor 233 is excited by the first color component light transmittedthrough the separation element to generate the second color componentlight. The optical system combines the first color component light madeincident on the separation element from the LD 101 and reflected by theseparation element with the second color component light made incidenton the separation element from the phosphor 233 and transmitted throughthe separation element. The separation element is configured to havevariable transmittance and reflectance with respect to the first colorcomponent light.

As a result, the spectral characteristic of blue light can selectivelybe improved with a simple configuration without requiring significantchanges in configurations of the existing devices.

According to the lighting apparatus and the projection-type imagedisplay apparatus of the first embodiment, the first color componentlight generated by the light source may linearly be polarized. Theseparation element includes the dichroic mirror 220 having the region ofthe dichroic coat layer 221 reflecting the first color component lightand transmitting the second color component light and the region of theAR coat layer 222 transmitting the first and second color componentlights, and the region of the AR coat layer 222 may be disposed insidethe region of the dichroic coat layer 221 and may have a size smallerthan the spot size of the first color component light incident on thedichroic mirror 220 from the light source. The dichroic mirror 220 maybe configured to be movable for switching whether or not the first colorcomponent light is incident on the region of the AR coat layer 222.

As a result, by using the simple configuration and operation of movingthe dichroic mirror 220, the spectral characteristic of blue light canselectively be improved with a simple configuration without requiringsignificant changes in configurations of the existing devices.

The light applied to the dichroic mirror 220 passes through the slit 214of the phosphor wheel device 210 and is further converted into asubstantially parallel and wide light beam by the condenser lens 111.Therefore, even when rotation unevenness and/or deflection of thephosphor wheel device occurs, the luminance of the light output from theprojection-type image display apparatus 1 is stable, so that theprojection-type image display apparatus capable of stable colorcomposition can be provided.

According to the lighting apparatus and the projection-type imagedisplay apparatus of the first embodiment, the dichroic mirror 220 mayhave the multiple AR coat layers 222, 223 different in size and may beconfigured to be movable for switching which of the multiple AR coatlayers 222, 223 the first color component light is incident on.

As a result, when combining the blue light and the green light with eachother, the intensity ratio of the color component lights can be changed.

According to the lighting apparatus and the projection-type imagedisplay apparatus of the first embodiment, the first color componentlight may be a blue light, and the second color component light may be acolor component light containing a green range.

As a result, the spectral characteristic of blue light can be improved.

According to the lighting apparatus and the projection-type imagedisplay apparatus of the first embodiment, the separation element mayreflect a color component light having a wavelength longer than thewavelength in the green range of the second color component light.

As a result, by integrating a filtering function into the separationelement, the filter wheel device etc. on the subsequent stage can bereduced in cost.

According to the lighting apparatus and the projection-type imagedisplay apparatus of the first embodiment, the light source may be asolid-state light source element.

As a result, the high-luminance projection-type image display apparatus1 can be provided.

The lighting apparatus and the projection-type image display apparatusaccording to the first embodiment may further include the phosphor wheeldevice 210 having the slit 214 over a predetermined angular range. Thefirst color component light is incident on the separation element fromthe light source via the slit. The optical system combines the firstcolor component light reflected by the separation element with thesecond color component light transmitted through the separation elementand passing through the slit.

As a result, the phosphor wheel device 210 can generate another colorcomponent light from the first color component light.

According to the lighting apparatus and the projection-type imagedisplay apparatus of the first embodiment, the phosphor may be disposedon the phosphor wheel device 250.

As a result, a rise in temperature of the phosphor due to excitationwith the blue light can be suppressed to stably maintain thefluorescence conversion efficiency.

Second Embodiment

In the first embodiment, a dichroic mirror is used for partiallytransmitting and partially reflecting the blue light. In a secondembodiment, description will be made of the case of using a half-waveplate and a polarization beam splitter instead of the dichroic mirror soas to partially transmit and partially reflect the blue light.

[2-1. Configuration]

FIG. 18 is a schematic diagram showing an exemplary configuration of aprojection-type image display apparatus 1D according to the secondembodiment. The projection-type image display apparatus 10D includes ahalf-wave plate 234, a polarization beam splitter 235, and a drivingdevice 230D instead of the dichroic mirror 220 and the driving device230 shown in FIG. 1.

The half-wave plate 234 rotates a polarization plane of the blue lightcoming from the condenser lens 111 over a predetermined angle. In anexample of FIG. 18, the blue light incident on the half-wave plate 234from the condenser lens 111 has P-polarized light similarly to the bluelight incident on the dichroic mirror 220 from the optical diffuser 105.

The polarization beam splitter 235 partially transmits and partiallyreflects a blue light depending on the polarization of the blue light.

The driving device 2300 rotates the half-wave plate 234 around anoptical axis. Rotating the half-wave plate 234 changes the polarizationplane of the blue light incident on the polarization beam splitter 235from the half-wave plate 234. As a result, the half-wave plate 234 andthe polarization beam splitter 235 are configured to have variabletransmittance and reflectance with respect to the blue light.

In this description, the half-wave plate 234 and the polarization beamsplitter 235 are also referred to as a “separation element”.

FIG. 19 is a graph showing an exemplary transmission characteristic ofthe polarization beam splitter 235 of FIG. 18. The polarization beamsplitter 235 transmits and reflects respective halves of an S-polarizedblue light having a wavelength of 465 nm incident thereon and transmitsand reflects respective halves of a P-polarized blue light having awavelength of 442 nm incident thereon. The polarization beam splitter235 transmits 96% or more of green and red lights regardless ofpolarization.

[2-2. Operation]

FIG. 20 is a schematic diagram showing a path of blue light when thespectral characteristic of blue light is improved in the projection-typeimage display apparatus 1D of FIG. 18. FIG. 21 is a schematic diagramshowing a path of blue light when the spectral characteristic of bluelight is not improved in the projection-type image display apparatus 1Dof FIG. 18. Specifically, as shown in FIG. 21, when all the blue lightincident on the polarization beam splitter 235 from the half-wave plate234 is S-polarized, all the blue light is reflected by the polarizationbeam splitter 235. On the other hand, as shown in FIG. 20, when thehalf-wave plate 234 is rotated to mix the S-polarized blue light withthe P-polarized blue light, a portion of the blue light is transmittedthrough the polarization beam splitter 235 and made incident on thephosphor 233 via the condenser lenses 231, 232. The green lightgenerated by the phosphor 233 reaches the dichroic mirror 106 as in thefirst embodiment so that the spectral characteristic of the blue lightcan be improved. In this way, the polarization characteristic of theblue light transmitted through the half-wave plate 234 (the mixing ratioof S-polarized light and P-polarized light) is changed by changing theangle of the half-wave plate 234. As a result, the reflectance and thetransmission ratio of the polarization beam splitter 235 is changed.

Depending on the rotation angle of the half-wave plate 234, the x-ychromaticity coordinates in the CIE1931 color space can arbitrarily bechanged along the broken line of FIG. 10.

[2-3. Effects]

According to the lighting apparatus and the projection-type imagedisplay apparatus of the second embodiment, the first color componentlight generated by the light source is linearly polarized. Theseparation element includes the half-wave plate 234 rotating thepolarization plane of the first color component light over apredetermined angle and the polarization beam splitter 235 partiallytransmitting and partially reflecting the first color component lightdepending on the polarization of the first color component light. Thehalf-wave plate 234 is rotatably disposed.

As a result, by using the simple configuration and operation of rotatingthe half-wave plate 234, the spectral characteristic of blue light canselectively be improved with a simple configuration without requiringsignificant changes in configurations of the existing devices.

Other Embodiments

As described above, the embodiments have been described asexemplification of the techniques of the present disclosure. For thispurpose, the accompanying drawings and detailed description areprovided.

Therefore, the constituent elements described in the accompanyingdrawings and the detailed description may include not only theconstituent elements essential for solving the problems but also theconstituent elements non-essential for solving the problems so as toexemplarily describe the techniques. Thus, it should not be immediatelyrecognized that these non-essential constituent elements are essentialsince these non-essential constituent elements are described in theaccompanying drawings and the detailed description.

In this description, the case of improving the spectral characteristicsof blue light has been described; however, the spectral characteristicsof other color component lights (red light, green light, etc.) can beimproved as well.

In this description, the case of using a laser diode the light sourcehas been described; however, for example, a light-emitting diode may beused as the light source. This enables reduction in costs of thelighting apparatus and the projection-type image display apparatus whenthe luminance thereof is reduced.

Although the case of the linearly moving dichroic mirrors 220, 220B hasbeen described with reference to FIGS. 5 and 14, the dichroic mirror mayrotationally move around any rotation axis.

The dichroic mirrors 220, 220B and the half-wave plate 234 may be movedor rotated by hand instead of the driving device.

Since the embodiments described above are intended to exemplarilydescribe the techniques of the present disclosure, variousmodifications, replacements, additions, and omissions can be made withinthe claims and the scope equivalent thereto.

According to the present disclosure, a spectral characteristic of acertain color component light can be improved in a lighting apparatusand a projection-type image display apparatus without significantchanges in configurations of existing devices.

What is claimed is:
 1. A lighting apparatus comprising: a light sourcegenerating a first color component light; a separation elementconfigured to partially transmit the first color component light,partially reflect the first color component light, and transmit a secondcolor component light different from the first color component light ata certain moment; an illuminant excited by the first color componentlight transmitted through the separation element to generate the secondcolor component light; and an optical system configured to combine thefirst color component light made incident on the separation element fromthe light source and reflected by the separation element with the secondcolor component light made incident on the separation element from theilluminant and transmitted through the separation element, wherein theseparation element is configured to have variable transmittance andreflectance with respect to the first color component light, the firstcolor component light generated by the light source is linearlypolarized, the separation element includes a dichroic mirror including afirst region reflecting the first color component light and transmittingthe second color component light and a second region transmitting thefirst and second color component lights, wherein the second region isdisposed inside the first region and has a size smaller than a spot sizeof the first color component light incident on the dichroic mirror fromthe light source, and the dichroic mirror is configured to be movablefor switching whether or not the first color component light is incidenton the second region.
 2. The lighting apparatus according to claim 1,wherein the first color component light is a blue light, and the secondcolor component light is a color component light including a greenrange.
 3. The lighting apparatus according to claim 2, wherein theseparation element reflects a color component light having a wavelengthlonger than a wavelength in the green range of the second colorcomponent light.
 4. The lighting apparatus according to claim 1, whereinthe light source is a solid-state light source element.
 5. Aprojection-type image display apparatus comprising: the lightingapparatus according to claim
 1. 6. A lighting apparatus comprising: alight source generating a first color component light; a separationelement configured to partially transmit the first color componentlight, partially reflect the first color component light, and transmit asecond color component light different from the first color componentlight at a certain moment; an illuminant excited by the first colorcomponent light transmitted through the separation element to generatethe second color component light; and an optical system configured tocombine the first color component light made incident on the separationelement from the light source and reflected by the separation elementwith the second color component light made incident on the separationelement from the illuminant and transmitted through the separationelement, wherein the separation element is configured to have variabletransmittance and reflectance with respect to the first color componentlight, the lighting apparatus further includes a first phosphor wheeldevice including a slit over a predetermined angular range, the firstcolor component light is incident on the separation element from thelight source through the slit, and the optical system combines the firstcolor component light reflected by the separation element with thesecond color component light transmitted through the separation elementand passing through the slit.
 7. The lighting apparatus according toclaim 6, wherein the first color component light is a blue light, andthe second color component light is a color component light including agreen range.
 8. The lighting apparatus according to claim 7, wherein theseparation element reflects a color component light having a wavelengthlonger than a wavelength in the green range of the second colorcomponent light.
 9. The lighting apparatus according to claim 6, whereinthe light source is a solid-state light source element.
 10. Aprojection-type image display apparatus comprising: the lightingapparatus according to claim 6.